An important seismic event imperceptible to humans has begun in the Pacific
Northwest as predicted, according to the government agency Geological
Survey
of Canada.
The chance of a major earthquake is 30 times higher now for a roughly
two-week period, but the odds are still remote, scientists say.
The event is called episodic tremor and slip (ETS). It involves a slow
movement of the Juan de Fuca and North America tectonic plates along the
Cascadia
http://www.livescience.com/forcesofnature/050103_cascadia_tsunami.html>>margin of southern British Columbia. Faults associated with the plates have
been the sites of major earthquakes -- akin to the colossal tsumani-causing
quake last December in Indonesia -- every 500 years or so, the geologic
record shows. The last such temblor in the area struck on Jan. 26 in the
year 1700.
Slow creep
The movement is slower than a traditional earthquake but more rapid than
the
normal creep associated with the fault. It runs in the reverse direction of
the normal creep.
The movement was predicted. Scientists recently learned that these ETS
events recur about every 14 months. It has been detected by Global
Positioning System instruments.
The event does not mean an earthquake is imminent, but geologists are eager
to study it and learn more and they say sooner or later an ETS event is
likely to trigger a major quake.
"Compared to the steady year-round stress accumulation, this more rapid
stress increase implies that a large subduction earthquake is more likely
to
happen during the time of an ETS event," the Canadian geologists write.
The slippage and associated minor tremors "are directly related to
megathrust (Sumatra-like) earthquake potential," lead geologist John
Cassidy
and a colleague said in Tuesday's statement. "Neither the tremor nor the
slip can be felt."
Odds go up
The slip began Sept. 3 on the Olympic Peninsula of Washington State and has
migrated north to the Vancouver Island area, Cassidy wrote. Victoria moved
0.12 inches (3 millimeters) to the West over the course of two days. The
events are thought to last six to 15 days.
Cassidy's colleague, Stephane Mazzotti, has done some calculations on the
odds of a large temblor.
"The probability of occurrence of a megathrust earthquake is about 30 times
higher during this approximately two-week window, than during the rest of
the 14.5 month cycle," Cassidy told LiveScience. "Having said that, 30
times
a small number is still a small number."
Geologists simply don't know when one of these events will trigger a major
quake, Cassidy said.
The immediate importance of the event is that it occurred as predicted and
can now be used to improve understanding of the region's seismology.
"By better understanding these events, we will be able to better predict
the
effects (and perhaps timing) of future magnitude 9 earthquakes along the
West Coast," Cassidy and his colleague write.
A separate
study recently concluded that a major earthquake along the fault could be
overdue, given clusters of the events seen in the geologic record. Because
the fault is offshore, scientists say its rupture could create a
devastating tsunami.
Phyllis has been harping on everyone to get their emergency kits ready. If in fact the big one hits here, we are right on the line so we will get hard!!! I took out earthquake insurance about 8 years ago, so I am not worried. I just do not want the island to sink under the North American plate. That could get kinda hairy.
I am not afraid of surviving, if I made it out of the house alive, but I would be terrible worried about the rest of the family. Phyllis is only up about 50 feet, I'm up about 150.
Well folks it is liable to get really interesting around here...Gee Thanks Kate!!
Seriously, Kate, thanks for the link. Good to see you up and about! ;)
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